workflow: sign commits (#4526)

This doesn't do much, but at least it doesn't litter PRs with non-signed
commits. This should keep the DCO clean(er)
Signed-off-by: Miek Gieben <miek@miek.nl>

.github/workflows/go.fmt.yml

@@ -31,6 +31,6 @@ jobs:
         run: |
           git add .
           if output=$(git status --porcelain) && [ ! -z "$output" ]; then
-            git commit -m 'auto go fmt'
+            git commit -s -m 'auto go fmt'
             git push
           fi

.github/workflows/go.tidy.yml

@@ -34,6 +34,6 @@ jobs:
         run: |
           git add .
           if output=$(git status --porcelain) && [ ! -z "$output" ]; then
-            git commit -m 'auto go mod tidy'
+            git commit -s -m 'auto go mod tidy'
             git push
           fi

.github/workflows/make.doc.yml

@@ -38,6 +38,6 @@ jobs:
         run: |
           git add .
           if output=$(git status --porcelain) && [ ! -z "$output" ]; then
-            git commit -m 'auto make -f Makefile.doc'
+            git commit -s -m 'auto make -f Makefile.doc'
             git push
           fi

.github/workflows/whitespace.yml

@@ -31,6 +31,6 @@ jobs:
         run: |
           git add .
           if output=$(git status --porcelain) && [ ! -z "$output" ]; then
-            git commit -m 'auto remove trailing whitespaces'
+            git commit -s -m 'auto remove trailing whitespaces'
             git push
           fi